add SIGSYS support to sys/signalfd.h from linux v4.18

new in linux commit 76b7f670730e87974f71df9f6129811e2769666e

in struct signalfd_siginfo the pad member is changed to __pad to keep
the namespace clean, it's not part of the public api.

include/sys/signalfd.h

@@ -35,7 +35,11 @@ struct signalfd_siginfo {
 	uint64_t  ssi_stime;
 	uint64_t  ssi_addr;
 	uint16_t  ssi_addr_lsb;
-	uint8_t   pad[128-12*4-4*8-2];
+	uint16_t  __pad2;
+	int32_t   ssi_syscall;
+	uint64_t  ssi_call_addr;
+	uint32_t  ssi_arch;
+	uint8_t   __pad[128-14*4-5*8-2*2];
 };
 
 #ifdef __cplusplus